It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, especially the intake valves, under certain engine load conditions. For a cam-in-block pushrod engine, a known approach to providing selective deactivation is to equip the hydraulic lifters for those valves with a locking mechanism whereby the lifters may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated pushrods. Typically, a deactivating hydraulic valve lifter (DHVL) includes, in addition to the conventional hydraulic lash compensation element, an outer body and a concentric locking pin housing disposed inside the outer body. The inner locking pin housing and outer body are mechanically connected to the pushrod and to the cam lobe, respectively, and may be selectively latched and unlatched hydromechanically to each other, typically by the selective engagement of one or more locking pins by pressurized engine oil.
U.S. Pat. No. 6,497,207 discloses such a DHVL wherein a lost motion coil spring is disposed between the lifter body and a tower extension of the inner pin housing. The tower extension is hollow and open at the outer end to admit an engine pushrod. This arrangement is functionally satisfactory for many but not all engine designs. In particular, the tower results in a relatively long overall length of the DHVL and, in order for the pushrod to clear the outer edge of the tower extension, the pushrod must be aligned nearly coaxial with the DHVL. Thus, this arrangement may be incompatible with engines having limited axial space for the added length DHVL, or for engines having relatively large pushrod engagement angles.
It is known in the art to shorten the operative length of a body and locking pin housing assembly by packaging the lost motion (LM) spring between the adjacent walls of the outer lifter body and the inner pin housing, thereby obviating the need for a tower and its concomitant length. U.S. Pat. No. 6,321,704 B1 (“the '704 patent”) discloses a hydraulic lash adjuster for valve deactivation in a cam-in-head roller finger follower engine having an outer body and an inner locking pin housing wherein the LM spring is disposed in an annular spring chamber between the walls of the body and locking pin housing.
A significant shortcoming of disposing the LM spring between the outer body and inner locking pin housing, as shown in the '704 patent, is that oil being supplied to the hydraulic element assembly (HEA) must pass through the LM spring chamber. Thus the chamber is always filled with oil, which must be pumped out of the chamber with every stroke of the lifter body in deactivation mode. Pumping oil reduces engine efficiency, as during at least part of the pumping stroke the oil pressure generated in the LM chamber opposes the engine's own oil pressure, and may cause valve train stability issues, wear, and noise due to induced air bubbles or cavitations. Still further, juxtaposition of the oil passages in the outer body and inner locking pin housing under certain lash conditions can allow for a low oil drawdown (drainage) level in the lash adjuster reservoir during engine shutdown, resulting in significant engine noise at restart.
In addition, the disclosure fails to account for mechanical lash in the deactivation mechanism resulting from inherent manufacturing variability in the deactivation components. The entire assembly is held together by a standard stop clip which is full-fitting in a groove in the outer body member. Thus, the amount of lash between the latching member and the latching surface after assembly, resulting from manufacturing variability in the components, cannot be compensated or adjusted in individual lifter or lash adjuster assemblies.
What is needed in the art is a deactivation lifter or lash adjuster assembly wherein the LM spring chamber is not in communication with the engine oil being supplied to the HEA.
What is further needed in the art is a deactivation lifter or deactivation lash adjuster assembly wherein mechanical lash within the lifter or lash adjuster may be readily set by appropriate shimming during assembly.
It is a principal object of the present invention to provide improved valve deactivation without pumping of deactivation oil in an LM spring chamber in engines requiring short overall length and large pushrod angle capability in a deactivation lifter or deactivation lash adjuster.